Harp of Hearts

A pluck of the strings sends an uncomfortable shiver through your heart. A gift from a demon of desire, it’s original owner played it for hours, hoping to save their beloved from death. Though their love was eternal, their lifespan was not.

I think I found a similar idea to this in an old 2nd edition DnD booklet of magic items. Powerful, but at a heavy price. Items that change the age of a character are rare it seems, but it can be just as much a number to keep track of as hitpoints or ability scores.

mechanics-wise, I would probably insist that the performer cannot do anything else beyond play. They can talk and move, but as soon as the music stops, the effect ends.